A~debug.js

// path/to/module/debug.js

var express = require('express');

exports.diagnostics = function() {    
    var app1 = express.createServer();
    
    app1.configure(function() {
        this.set('view engine', 'ejs');
        this.set('views', __dirname + '/views/app1');
        this.set('view options', { layout: false, open: '{%', close: '%}' });
    });
    
    app1.mounted(function(host) {
        host.dynamicHelpers({
            app1inc: function(req, res) {
                return function(ctx) {
                    // XXX res.app is app1, so this fails...
                    // the intention is that the app we're mounted in
                    // should get the content from our bundled include
                    return res.partial('_include.ejs', { object: ctx, as: 'foo' });
                }
            }
        });
    });
    
    app1.get('/', function(req, res) { res.render('index.ejs'); });
    
    return app1;
};

A~views~index.ejs

<!-- path/to/module/views/index.ejs -->
<!-- served at: http://localhost:3000/debug/index.ejs -->
<div>packaged app index</div>
<!-- this partial works fine: -->
<%- partial('include.ejs', { object: { test: 'hosted' }, as: 'foo' }) %>

A~views~partials~include.ejs

<!-- path/to/module/views/partials/include.ejs -->
<div>packed app include: foo.test is {%= foo.test %}</div>

B~app.js

// ./apps.js: main app

var express = require('express');
var debug = require('debug');

var app2 = express.createServer();

app2.configure(function() {
    this.set('view engine', 'ejs');
    this.set('views', __dirname + '/views/app2');
    this.set('view options', { layout: false });
});

// uses packaged 'debug' app
app2.use('/debug', debug.diagnostics());

app2.get('/', function(req, res) { res.render('index.ejs'); });

if (! module.parent) {
  app2.listen(3000);
  console.log("Express server listening on port %d", app2.address().port);
}

B~views~index.ejs

<!-- ./views/index.ejs -->
<h1>App 2</h1>
<p><%- app1inc({ test: 'app2' }) %></p>